Tanzania is one of the countries in sub-Saharan Africa that is severely affected by the HIV epidemic. Despite substantial progress over the past decade, large gaps in implementing efficacious and safe HIV interventions remain - e.g., in male medical circumcision coverage and antiretroviral treatment (ART) and prevention of mother-to-child transmission (PMTCT) uptake, retention and adherence. At the same time, funders are increasingly demanding evidence on the population health impact of their investments; and national policy makers are struggling with questions how to ensure financial and operational sustainability of HIV programs within the context of the Tanzanian health system. To find solutions to these challenges, we need rigorous Implementation Science, Impact Evaluation, and Health Systems Research to test alternative models to deliver HIV interventions and establish their comparative feasibility, acceptability, effectiveness, and cost-effectiveness. However, the scientists to carry out such research projects are currently lacking in Tanzania. This program thus aims to (1) train a critical mass of mid-level and senior researchers to (a) work as principal investigators leading independent research programs focused on questions of HIV program implementation and evaluation and (b) teach HIV-related Implementation Science, Impact Evaluation, and Health Systems Research in Tanzania; (2) build a critical mass of junior public health and medical professionals who can design and successfully carry out rigorous research projects in HIV Implementation Science, Impact Evaluation, and Health Systems Research; and (3) develop a sustainable Master's program in HIV Implementation Science and Impact Evaluation in Dar es Salaam. This training program will be collaboration between the Harvard School of Public Health (HSPH) in Boston and Muhimbili University of Health and Allied Sciences (MUHAS) in Dar es Salaam. Based on an in-depth needs assessment, we identified training gaps in three principal areas: HIV interventions; health systems and implementation; and research methods, including Implementation Science, Impact Evaluation, Health Economics, and Biostatistics. We have recruited training and mentoring faculty with practical and theoretical experience in these areas, as well as experienced colleagues for the Executive and the Training Advisory Committees. The primary training strategies in this program will comprise of (1) two-year post-doctoral fellowships in Boston and Dar es Salaam; (2) short-term fellowship training in Boston with ongoing mentoring; (3) intensive courses (which will serve as building blocks for the Master's program at MUHAS); and (4) research symposia. In total, the program will train 10 two-year post-doctoral fellows; 22 short-term post-doctoral fellows (12 post- and 10 pre-doctoral); and provide intensive short course instruction to 240 individuals.